Electronic vapor provision systems, electronic nicotine delivery systems, etc, which are collectively referred to herein as e-cigarettes, generally contain a reservoir of liquid which is to be vaporized. When a user sucks or draws on the device, this activates a heater to vaporize a small amount of liquid, which is then inhaled by the user. Most e-cigarettes include a re-chargeable battery for supplying electrical power to the heater and other electrical/electronic components, such as a sensor to detect inhalation. Some e-cigarettes have a cartridge section. After the nicotine or other liquid in this cartridge has been exhausted, the empty cartridge can be removed or separated from the e-cigarette and replaced with a new cartridge containing further nicotine.
E-cigarettes are often supplied in packs for protection and easy portability. Such packs may accommodate multiple e-cigarettes and/or replacement cartridges, thereby offering a backup facility if one e-cigarette (or its cartridge) is exhausted. An e-cigarette pack may also have the ability to re-charge an e-cigarette, again helping to ensure good operating availability of the e-cigarette for a user. Typically a pack is provided with a cylindrical hole for receiving an e-cigarette for recharging, the hole generally reflecting the elongated, cylindrical shape of an e-cigarette. When the e-cigarette is located in the hole, the battery can be re-charged by a suitable wired or wireless connection (a wireless connection may rely upon induction charging). In some packs, the cylindrical hole may receive the entire e-cigarette for re-charging, while in other packs only a portion of the e-cigarette may be received into the hole.
In some devices, the pack must be connected to a power supply, e.g. a mains outlet or USB connection, during re-charging of the e-cigarette battery. In this case, the pack is typically acting as a convenient device for holding and interfacing to the e-cigarette during re-charging. In other devices, the pack itself is provided with a battery (or other charge storage facility). The pack battery allows the e-cigarette to be re-charged from the pack without the need for the pack to be connected to an external power supply during the re-charging, thereby providing greater convenience for a user.
The pack battery will be depleted in due course, and so is generally provided with its own re-charging facility—typically again reliant upon some form of mains or USB connection. However, since the pack is larger than an e-cigarette, it can accommodate a larger battery and therefore the pack does not have to be re-charged as frequently as an e-cigarette. For example, the charge capacity of a typical e-cigarette battery may be approximately 60 mAh, whereas the charge capacity of a typical pack battery might be in the region of 800 mAh. Accordingly, the pack battery is capable of re-charging the e-cigarette a few times at least before the pack battery itself needs to be re-charged.
Such a multiple or hierarchical arrangement of separately chargeable systems, namely firstly an e-cigarette and secondly a pack for the e-cigarette, is relatively rare. In contrast, most re-chargeable devices, e.g. mobile (cell) phones, are usually connected directly to a mains-powered charging supply (or else to an in-car charging supply).
It is desirable for the operation and (re)charging of an e-cigarette and associated pack to be as safe, reliable and convenient for a user as possible. One potential concern relates to the lithium ion batteries that are used in many types of device, including e-cigarettes, because of their high energy density. If such a battery is defective, it may, on rare occasions, catch fire —see, for example, the news article dated 4 Feb. 2014 entitled “Batteries on planes pose ‘increased fire risk,’” available at www.bbc.co.uk. Although some existing e-cigarettes may incorporate certain safety features to address such issues, these have generally been incorporated in an ad hoc (rather than systematic) manner.